Nanoplasmonic device with nanoscale cooling

ABSTRACT

A nanoplasmonic device includes a nanoplasmonicly heatable layer having a heating side and a cooling side, the heatable layer including a plurality of localized energy receiving sites; and a cooling structure located adjacent to the cooling side, the cooling structure including a nanoscale structure to remove heat from the heated layer.

BACKGROUND OF THE INVENTION

The present invention relates to nanoplasmonic devices and, inparticular, to the cooling of nanoplasmonic devices.

Nanoplasmonic techniques are being used increasingly to couple opticalenergy into devices. Examples of such applications include magneticmemory, photovoltaic cells, and sub-wavelength lithography. Besidesefficient coupling of the energy, sub-wavelength resolutions arepossible.

Such applications make use of an optical spot smaller than thediffraction limit. This can result in substantial localized heating.Heat can be removed with a bulk metallic layer, but this can result ingeneral heating by spreading the heat and may as well change thenear-field characteristics of the device. In general, it may bedifficult to obtain satisfactory cooling in an efficient and compactmanner.

SUMMARY OF THE INVENTION

A nanoplasmonic device includes a nanoplasmonicly heatable layer havinga heating side and a cooling side, the heatable layer including aplurality of localized energy receiving sites; and a cooling structurelocated adjacent to the cooling side, the cooling structure including ananoscale structure to remove heat from the heated layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example of a nanoplasmonic systemaccording to an aspect of the invention;

FIG. 2 is a schematic diagram of an example of a nanoplasmonic deviceaccording to another aspect of the invention;

FIG. 3 is a schematic diagram of an example of a nanoplasmonic deviceaccording to an additional aspect of the invention; and

FIG. 4 is a schematic diagram of an example of a nanoplasmonic deviceaccording to another additional aspect of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an example nanoplasmonic system 10 includes opticalsources 12, nanotransducers 14, and a nanoplasmonic device 20.

The nanoplasmonic device 20 includes a heatable layer 22 having aheating side 24 and a cooling side 26 and a cooling structure 28adjacent to the cooling side 26. The cooling structure 28 includesnanostructures described more fully below.

The heatable layer 22 may be, for example, a magnetic memory materialresponsive to heat, a photovoltaic cell, or a lithography material.

In operation, each optical source 12 and nanotransducer 14 combinationcan produce a sub-wavelength spot 16 of optical energy on the heatablelayer 22. The nanotransducers 14 may be, for example, known devices forlocalizing incident radiation into a sub-wavelength heated spots such asnanoparticles, nanoantennas and nanowaveguides. Each spot 16 correspondsto a localized energy receiving site. would also be possible totranslate a single optical source 12 and nanotransducer 14 combinationto successively illuminate the spots 16. Radiative heat transfer at thenanoscale is the fundamental mechanism in coupling the sub-wavelengthoptical spots 16 produced by each optical spot 12 and nanotransducer 16combination.

When two objects are not in contact, i.e. when these two objects areseparated by a distance, there is still a heat transfer between objectsdue to radiative heat transfer. The heat is transferred between thesetwo bodies through electromagnetic radiation. Classically, thiselectromagnetic radiation from an object is related to the temperatureof the object, and is known as the blackbody radiation. Theelectromagnetic radiative heat transfer from an object to another objectnot only depends on the temperature of the radiator, but also otherfactors as well, including the distance between two objects.Electromagnetic radiation from an object scales with 1/R, where R is thedistance from the object. The electromagnetic power scales with 1/R̂2.

However, at the nanoscale, that is, the sub-wavelength scale, whenobjects are separated by less than sub-wavelength scale, the radiativeheat transfer between the surfaces can be several orders of magnitudehigher than predicted by Planck's blackbody radiation. The radiativeheat transfer at sub-wavelength distances can be three orders ofmagnitude higher than the prediction by Planck's blackbody radiation.This enhancement is due to electromagnetic energy tunneling of theevanescent fields, and excitation of surface plasmon or phononpolaritons on the structures. There are several ways to enhance thisradiative heat transfer between objects. When the objects are broughtinto the sub-wavelength near-field regime, the radiative energy transferbetween objects is enhanced due to evanescent coupling of theelectromagnetic energy between objects. This phenomenon is also referredto as photon tunneling, and it is observed if the objects are separatedby less than the wavelength of light. In addition, surface plasmonresonances or phonon resonances also improve the electromagnetic energytransfer. If the structures support surface plasmon resonances orsurface phonon resonances, the electromagnetic energy transfersubstantially increases. As used herein, plasmonic cooling or phononiccooling correspond to cooling an object through enhanced energy transferwhen one or more of the structures supports surface plasmon resonancesor surface phononic resonances, respectively.

While the space or gap between objects may be, for example, air orvacuum, material such as dielectrics may also be used.

Referring to FIG. 2, the nanoplasmonic device 20 includes a heatablelayer 22 and a cooling structure 28′ formed on a substrate 30. Thesubstrate may be for example a semiconductor or dielectric material suchas silicon or any other suitable material such as ceramic glass oramorphous glass and is generally much thicker than the other layers. Theheatable layer may be, for example, 5 nm to 30 nm thick. The coolingstructure 28′ may be, for example, 5 nm to 200 nm thick.

The cooling structure 28′ is formed from a dielectric or semiconductor32 with embedded nanoparticles 34 that support surface plasmon or phononresonance.

The size of the nanoparticles 34 can be between 5 nm and 200 nm. It isexpected that particle sizes on the order of 5 nm to 20 nm ispreferable. The alternating pattern of particles as a percentage oftotal width can be referred to as the duty cycle. A typical duty cyclefor the particles is around 50 percent.

The dielectric 32 can be, for example, an oxide such as silicon dioxide,titanium dioxide, or tantulum pentoxide. The nanoparticles 32 can bemade of metals such as gold, silver, aluminum, platinum, or copper tosupport surface plasmon resonances. Alternatively, the nanoparticles 32can be made of SiC, cubic boron nitride (cBN), hexagonal boron nitride(hBN), or boron carbide BC to support surface phonon resonances.

These structures can be fabricated using different techniques. Onepotential way to fabricate these structures is the thin-film depositionand patterning techniques, which are well-known and heavily utilized bysemiconductor companies and hard-disk drive companies. Thin film layerscan be deposited using different techniques such as sputtering, thermalevaporation, or ion beam deposition. The patterning of these structurescan be achieved using photolithographic techniques. Alternatively,patterning of these structures can also be achieved using more recentlydeveloped techniques including self-ordered arrays or nanoimprintlithography.

Different patterns can be made of nanoparticles embedded into adielectric or semiconductor layer. Different patterns can be obtained byusing different duty-cycles between particles. Also, different patternsinclude the possible shapes that can form the cross section of thelayer. Different patterns can refer to different cross sections ofnanoparticles, including, for example, spherical, cylindrical,rectangular and square. Different patterns can also refer to differentarrangements of these particles with respect to each other, includingregular distribution with constant duty-cycle and random distribution.

This utilizes the coupling between fundamental electromagnetic andthermal phenomena. Placing patterned structures that can support surfaceplasmon resonances and phonon resonances improve the localizedelectromagnetic and optical field distribution around these regions.Such localized and improved optical fields improve the radiative energytransfer between these particles and the heatable layer therebyimproving the localized heating and cooling.

Referring to FIG. 3, the nanoplasmonic device 20 includes a heatablelayer 22 and a cooling structure 28″ formed on a substrate 30. Thesubstrate may be for example a semiconductor or dielectric material suchas silicon or any other suitable material such as ceramic glass oramorphous glass and is generally much thicker than the other layers. Theheatable layer may be, for example, 5 nm to 30 nm thick. The coolingstructure 28″ may be, for example, 5 nm to 200 nm thick.

The cooling structure 28″ includes a gap 36 between the heatable layer22 and the polariton layers 38, 40, 42, 44. The gap 36 facilitates theradiative energy transfer between the layers. This gap should be verysmall, i.e. nanoscale scale or sub-wavelength scale, to facilitatephonon tunneling (or evanescent energy coupling) between the structures.The layer underneath is selected so that it supports surface phononresonances or alternatively it can be selected to support surfaceplasmon resonances. This way the radiative energy transfer between theobjects is further enhanced.

The polariton layers 38, 40, 42, 44 are a multilayer structure, whereeach layer may have a different thickness and material property. Eachlayer may have a different property from the other. The stack supportssurface plasmon resonances or surface phonon resonances. These aresurface waves that can be excited under specific conditions. The layerscan be surface plasmon resonance supporting metals such as gold orsilver; or surface phonon resonance materials such as SiC, cubic boronnitride (cBN), hexagonal boron nitride (hBN), or boron carbide BC. Inbetween the layers are dielectric layers.

Referring to FIG. 4, the nanoplasmonic device 20 includes a heatablelayer 22 and a cooling structure 28′″ formed in the substrate 30.

The cooling structure 28′″ includes sub-micron channels 46 in thesubstrate 30 for use with a circulating cooling fluid, for example,water. Inside of each channel 46 are nanorods 48 to improve heatabsorption by the cooling fluid. Shapes other than rods could also beemployed.

The cooling structure 28′″ may be, for example fabricated in a siliconsubstrate. The substrate 30 can be formed from two halves anodicallybonded together and similarly bonded to the heatable layer 22. E-beamlithography techniques can be used to form the channels in each half.Before bonding, the nanostructures can be deposited by glancing angledeposition (GLAD). The nanostructures can be rods of copper for example.

It should be noted that the cooling structure 28′″ is localized underthe spot 16. This localization can be employed in the other embodimentsherein as well. This allows not only the more rapid cooling possiblewith nanoscale structures, but also the focusing of the cooling effectsmore closely to where they are needed.

It should be evident that this disclosure is by way of example and thatvarious changes may be made by adding, modifying or eliminating detailswithout departing from the fair scope of the teaching contained in thisdisclosure. The invention is therefore not limited to particular detailsof this disclosure except to the extent that the following claims arenecessarily so limited.

What is claimed is:
 1. A nanoplasmonic device comprising: ananoplasmonicly heatable layer having a heating side and a cooling side,said heatable layer including a plurality of localized energy receivingsites; and a cooling structure located adjacent to said cooling side,said cooling structure including a nanoscale structure to remove heatfrom said heated layer.
 2. A nanoplasmonic device according to claim 1,wherein said cooling structure comprises a plasmonic cooling layer.
 3. Ananoplasmonic device according to claim 2, wherein said plasmoniccooling layer comprises longitudinally alternating nanoparticles andnon-nanoparticle regions.
 4. A nanoplasmonic device according to claim2, wherein said plasmonic cooling layer comprises a gap layer of lessthan a sub-wavelength thickness and a plasmonic sub-layer.
 5. Ananoplasmonic device according to claim 4, wherein said plasmoniccooling layer comprises alternating gap layers and plasmonic sub-layers.6. A nanoplasmonic device according to claim 1, wherein said coolingstructure comprises a phononic cooling layer.
 7. A nanoplasmonic deviceaccording to claim 6, wherein said phononic cooling layer compriseslongitudinally alternating nanoparticle and non-nanoparticle regions. 8.A nanoplasmonic device according to claim 6, wherein said phononiccooling layer comprises a gap layer of less than a sub-wavelengththickness and a phononic sub-layer.
 9. A nanoplasmonic device accordingto claim 8, wherein said phononic cooling layer comprises alternatinggap layers and phononic sub-layers.
 10. A nanoplasmonic device accordingto claim 1, wherein said cooling structure comprises sub-micron fluidpassages including nanostructure heat-absorbing structures.
 11. Ananoplasmonic device according to claim 1, wherein said coolingstructure is localized to said localized energy receiving sites.
 12. Ananoplasmonic device according to claim 1, wherein said device is one ofa data storage device, a photovoltaic cell and a lithography medium.